Codeposition of metallics and non-metallics



Jan. 6, 1970 J, scHMm'r I 3,488,263

CODEPOSITION 0F METALLICS AND NON-METALLICS Filed April 22, 1968 INVENTORI FERENC J SCHMIDT,

BY WW United States Patent 3,488,263 CODEPOSITION OF METALLICS AND NON-METALLICS Ferenc J. Schmidt, Ardmore, Pa., assignor to General Electric Company, a corporation of New York Filed Apr. 22, 1968, Ser. No' 722,957

Int. Cl. C23b 13/00; B01k 5/02; C23f 17/00 US. Cl. 204-38 3 Claims ABSTRACT OF THE DISCLOSURE Material to be included in electroplate is suspended in plating solution. Potential applied to plating cell is varied periodically between: a value at which normal plat ng current density, appropriate to particular work, flows; and a value beyond that required to produce concentration-polarization-limited current density, sufficient to produce electrophoresis of material to be included toward layer being plated. Higher value of voltage may typically be of order of 25 to 50 volts.

BACKGROUND OF THE INVENTION Field of the invention This invention pertains to the art of electroplating.

Description of the prior art Various suggestions have been made, and some have been applied, that solid matter be suspended in an electroplating bath so that it will be included in the deposit being electroplated. The material to be included may be intended to reinforce the plated material, or to provide some property, such as magnetic permeability or abrasiveness or radioactivity which the electroplate does not have and which may constitute an additional virtue in the electroplate, or may be the desired property for which the electroplate provides a convenient carrier. The inclusions, being macroscopic, ordinarily difiuse much more slowly than the ions being reduced to metal; and, having ordinarily a much smaller ratio of charge to mass than do the ions, they are not driven perceptibly by the comparatively weak fields which ordinarily sufiice to provide a desirable plating current density. Thus it is not easy to produce either a great or an arbitrarily variable density of inclusions in a plate by the prior art methods. It has, indeed, been proposed and attempted to provide a large concentration of inclusions immediately adjacent to a layer being plated by providing a rapid circulation of electrolyte with inclusions in suspension, the circulation permitting a higher concentration of inclusions; but this same circulation reduces the probability of a particle being trapped against the Surface being plated, so that its benefits may be more illusory than real.

SUMMARY In Introduction to Electrochemistry, Samuel Glasstone, D. Van Nostrand Company, Inc., copyright 1942, sixth printing, at page 448, Fig. 113 represents generally the relation between current density and electrode potential in an electrolytic cell, showing that with increasing applied potential the current density rises until it reaches a so-called limiting current density, which remains nearly constant with a considerable range of potential increase. It is explained in the accompanying text, extending from page 445 through page 452, which is incorporated herein by reference, how the limiting current density is believed to be determined by the rate at which reactant ions can be furnished by transport and difiusion to the layer adja' cent the electrode. It is further explained that the potential will increase without increase in current density until a potential value is reached at which some other process occurs, e.g. the dissociation of the aqueous solvent. While it is not so stated, it is clear that that other electrolytic process, too, will have a limiting current density at which a wide variation of potential will be possible without marked variation in current density.

I have found that it is possible to provide a plating bath in which there is suspended at least partly colloidally, i.e. by charges thereupon, material which is to be included in a metal to be plated out of the plating bath; and to apply for a first period, to a plating cell containing such a bath and material, a first potential which produces a current density suitable for plating out such a metal; and then for a second, ordinarily much briefer, period a second, higher, potential sufficient to produce a current of limiting density and also sufficient to produce, adjacent to the electrode on which the metal is being plated, an electric field sufficiently great to cause the material to be deposited by electrophoresis upon the plated metal; and then to repeat the application of the first potential so as to plate more metal upon the metal previously plated so that it surrounds the material electrophoretically deposited. Alternate applications of the first potential to plate the metal under conditions desirable for that purpose, and of the second potential to deposit material, will result in the formation of a deposit of plated metal containing inclusions of the material.

The utility of such composite deposits is known. For example, abrasive material may be included in a metal matrix to form a lap which does not require external addition of abrasive, the wearing away of the metal exposing additional abrasive during use. Similarly, carbon (or other alloying material) may be incorporated in the composite of metal so that the composite may be heat treated to cause the inclusions to form an alloy with the plated metal; this may be useful in providing an alloy of greater hardness than the metal which can be plated directly.

I have found that by the practice of my invention it is feasible to produce such high concentrations of included pigments in a metal deposit that the pigment efiectively determines the apparent color of the deposit; and, since the pigment inclusions may extend throughout the deposit, the effect is of a permanently colored composite, whose color is not destroyed by wearing away of the surface.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THS PREFERRED EMBODIMENTS In FIG. 1, a conventional electrolytic tank 12 of any convenient solution-resistant insulating material (for example, a large battery jar) contains an electrolytic plating bath 14 which, in addition to the metal compounds characteristic of the plating bath, contains a suspension of material to be included in electroplate. A motordriven stirrer 16 is represented mounted on an edge of tank 12, with its propellor shaft extending down into the bath '14. Depending upon the nature of the suspended material more or less uniformly suspended in the bath, the suspended material must carry a charge, in the usual fashion of colloidally suspended materials; 'but for the practice of my invention it is preferable that the sign of the charge be such that the particle will be attracted to an electrode whose potential is of the proper sign to reduce the metal ions providing the metal to be plated out.

In general, metal is plated out at the cathode, and thus the suspended material should preferably carry a positive charge.

An anode 18 is represented hung, in conventional fashion, from a bar 20; and similarly a workpiece 22 is represented hung by a hook 24 from a bar 26. Bar 26 is connected by conductor 28 to the common negative terminal of a plating power supply 30. Bar 20 (and hence anode 1-8) is connected by conductor 32 to the center blade 34 of a motor-driven cam-operated switch 36. Switch 36 comprises a conventional motor 38 which rotates a cam 40. Cam 40, through follower 42 drives push rod 44 in guide 46, so that it moves blade 34 alternately to contact fixed blades 48 and 50. Since blades 48 and 50 are connected to two difierent positive terminals of plating power supply 30, the operation of motor 38 causes the alternate application to the cell represented of the two different potentials available from the two different positive terminals of supply 30. As represented, connection to the upper blade 48 will endure for a larger proportion of the time (as may be seen by inspection of the lobes of cam 40); and in this condition, the normal potential required ordinarily for plating will be applied. Connection to the lower blade 50 will endure for a smaller fraction of elapsed time, and will apply to the cell a much higher potential, so great that it produces a depletion of the ions immediately adjacent to the workpiece 22 by removing them by the high electric field faster than they can drift and diifuse in by normal processes. This depletion produces eifectively a double layer of ionic charge at the boundary of the depletion layer, and of charge in the surface of the workpiece. In this double layer, there is a very strong field which electrophoretically moves the suspended material, by the charge upon it, to the workpiece, where it is discharged and becomes attached. The subsequent restoration of normal applied potential (by rotation of cam 40, and upward movement of blade 34) permits ordinary electroplating again.

The product resulting from the operation of this process is represented schematically by FIG. 2, in which a substrate 52 is plated with a plating 54 which includes particles 56.

In actual practice of my invention, pigments employed were fine particles (100-300 mesh) of Ultramarine blue, and similarly ground white porcelain. These, suspended as charge-bearing particles in either the ethereal aluminum plating solution of Brenner, or a more conventional sulfamate nickel plating bath, could be deposited by electrophoresis by applying from to 25 volts for five seconds out of ever minute otherwise devoted to normal plating. 1

Specifically, with a sulfamate nickel plating bath of composition:

Ounces/gallon Nickel sulfamate 60 Boric acid 4.0 .005

Anti-pitting agent pH, 4.2.

the following was observed. The bath was operated at 90 degrees F., instead of the more conventional 115-130 degrees F., since limiting current density increases with increasing temperatures, and it is desirable to have the limiting current, which is produced when the high voltage is applied, within reasonable bounds. Normal nickel plating occurred up to 120 amperes per square foot. At 200 amperes per square foot (A.S.F., by conventional abbreviation) nickel deposited lacked the smoothness and luster of conventional plating, indicating that limiting current density was being approached; but'no pigment'was de posited. At 450 amperes per square foot pigment deposited but no noticable quantity of nickel (compatibly with an actual depletion of the nickel ions in the vicinity of the cathode) and at 600 A.S.F. good pigment deposit occurred. An actual product was made by continuing a cycle of 55 seconds at 120 A.S.F. for plating and 5 seconds of 600 A.S.F. pigment deposition. No occlusion was obtained with the 55-second period devoted to plating at only ASP. It would appear that too slow a plating operation permits the pigment to become resuspended in the solution, efiectively washing otf the workpiece. However, as amatter of practical economics, one usually plates as rapidly as is consistent with the desired deposit characteristics, so that this does not constitute in practice a limitation uponthe proces.

' It is worthy to mention that, when a blue pigment is used, this imparts a blue appearance to the product, so that it is possible to produce plated or electroformed parts which have the equivalent of a permanent colored finish. This is very desirable for many consumer products, such as automobile trim and accessories.

While the examples given cited a first period of time of fifty-five seconds for applying a first potential, and a second period of time of five seconds, for applying a second potential, it is evident that the absolute duration, and the ratio of the two periods of time, may be adjusted in accordance with the speed of plating of the metal to be plated, and the concentration of inclusions desired.

I claim:

1. In the method of making a composite of metal having fine particles included therein which comprises the steps of (a) providing a bath for electroplating the 'said metal which has the said fine particles suspended therein as positive charge-bearing particles, and (b) immersing a first electrode and a second electrode in the said bath and applying a potential between the said electrodes to plate the said metal on the said first electrode'with inclusions of the said fine particles; the improvement which comprises (0) adjusting the potential for a first period of time to a first value which produces a current density suitable for plating the said metal, and

(d) adjusting the potential for a second period of time to a second value which produces a limiting value of current density and causes the deposition by electrophoresis of said fine particles upon the metal plated on the first electrode, and

(e) repeating the performance of steps (0) and (d) alternately to form a composite.

2. The method of claim 1 in which the second value of potential is at least 10 volts. I

3. The method of claim 1 in which the fine particles are a colored pigment.

References Cited UNITED STATES PATENTS 3,356,467 12/ 1967 Brown et al. 29--l94 3,268,424- 8/ 1966 Brown et al. 204-41 JOHN H. MACK, Primary Examiner R. L. ANDREWS, Assistant Examiner US. Cl. X.R. 204-181 I 

